The evidence about physical activity and/or physical fitness as risk characteristics for coronary heart disease (CHD) is fraught with inadequacies in the design of studies and the information collected. These inadequacies may explain contradictory findings reported. In one study of physical activity and /or physical fitness, the United States Railroad Study (USSR), a unique combination is available of complete CHD risk factor ascertainment, estimates of leisure time and occupational physical activity, and an objective measure of physical fitness (a standardized exercise test). The USSR is a prospective study of 2571 men initially aged 40-59 employed by 20 railroad companies operating in the northwestern United States. Nearly 70% of a sample of all executives, dispatchers, switchmen, and clerks employed by these companies in 1957 was examined, first between 1957-1960, and again between 1962-1965. The USSR is a component of the International Cooperative Study of Cardiovascular Epidemiology (Seven Countries Study). Complete mortality followup has been accomplished through 10 years post-enrollment with data from the Railroad Retirement Board. It is proposed to study, in year 2 of this project, the relationships among CHD risk factors, physical activity, physical fitness, and mortality due to CHD. Such analysis will be made possible during year 1 of the project. Not only is this information needed to elucidate the nature and degree of any role of physical activity and fitness in CHD, but the study is timely in this period when professional public awarness is increasing of CHD risk factors and the potential for prevention of CHD.